A traditional knee-ankle-foot orthosis (KAFO) is used to increase the patient stability during the weight-bearing phase of walking. A traditional KAFO locks the knee in full extension, which provides stability. This locked posture results in patients' ability to ambulate with gait deviations that can lead to overuse injuries. A stance control orthosis (SCO) allows the knee to flex during the swing phase of the gait cycle and prevents knee flexion for stability during the stance phase. By allowing the knee to bend during the swing phase, SCOs allow a more natural gait, which may reduce secondary complications from gait compensations and allow the patient to walk with less effort.
FILLAUER® developed a gravity-actuated knee joint locking system for its Swing Phase Lock (SPL) orthosis (U.S. Patent 2003/0153854). A Swing Phase Lock uses a simple internal pendulum mechanism mounted on the thigh link (the member that moves in unison with the user's thigh). As the thigh link moves, the pendulum swinging motion locks and unlocks the shank link (the member that moves in unison with the user's shank) relative to the thigh link. This allows for locking and unlocking of the knee joint for appropriate phases of a walking cycle.
Free Walk orthosis (marketed by OTTOBOCK®) and UTX orthosis (marketed by BECKER®) work based on the principle. The dorsiflexion of the foot at the end of the stance pulls on controllable cable connected to a locking mechanism at the knee joint. This pulling action disengages the locking mechanism for swing. The locking mechanism is spring loaded and locks the knee when the knee is fully extended.
Sensor Walk (manufactured by OTTOBOCK®) uses a wrap spring at the knee joint for locking and unlocking the knee. This orthosis includes two sets of sensors—one at the knee to measure the knee angle and another at the footplate to measure force between the foot and the floor; a wrap spring clutch replacing the lateral knee joint to provide braking capability to support the anatomic knee joint; a microprocessor-controlled release for the brake; electronic circuitry; and a battery pack carried in a waist pack. Sensors in the footplate disengage the wrap spring clutch and allow the knee to bend in the late stance phase, when weight has been transferred to the contralateral side and is ready for single-limb support. A knee sensor senses extension of the knee after toe off and sends a signal to the microprocessor putting the wrap spring clutch in its locked position.
Horton Stance Control Orthosis (U.S. Pat. No. 6,635,024) includes a locking mechanism that locks and unlocks the knee with the help of a push rod. The push rod is placed between the heel and the knee. The push rod locks the knee at heel strike and unlocks the knee right at the end of stance phase. The device locks knee at any angle.